According to the pouring technology of molten metal, casting is classified into gravity casting and pressure casting. Gravity casting is that molten metal is injected under impact of gravity. It is also called as molding. Broad gravity casting contains sand casting, metal casting, investment casting and mud casting. Narrow gravity casting only refers to metal casting. Pressure casting refers to that molten metal is injected into mold under the pressure of other external forces (except for gravity). Broad pressure casting includes pressure die casting and vacuum casting on die-casting machine, low pressure casting and centrifugal casting. Narrow pressure castings only refers to metal pressure casting on die casting machine, also called as die casting. At present, non-ferrous metal casting is commonly used and has the least price.
Properties of gravity casting
1. Gravity casting is also called as metal mold casting. The principle is that the gravity on riser is used to supplement solidification and shrinkage. Gravity casting mold can be used repeatedly, also called as permanent mold casting.
2. Cooling method is to use compressing air (air cooling) or mist mixed with air and water to cool the mold and casting.
3. Measured processing should be kept on castings. Because castings may deform after being heated.
4. Degasification in aluminum water is also important. Otherwise, pinholes are easily caused on the surface of castings after being heated.
5. Metal casting is quite suitable for manufacturing orders having less quantity, while variety.
The differences between gravity and die casting
Due to principle and materials of mold, die casting is limited used for liquid forming of nonferrous metal while gravity casting does not have the limitation.
Structure of mold: cavity of die casting mold is located at the top of gating system. It needs assistance of injection machine during operation; gravity casting molding has different designs. And it is more advanced than die casting mold.
Materials of mold: the cavity of die casting mold often adopts metals having higher melting point and price. Gravity casting mold usually uses sand.